The present invention refers to a gas-dynamic pressure wave machine according to the preamble of the independent claims.
Such a pressure wave machine is known from the prior art, e.g. from CH-A-681 738. It is a first general object of the present invention to improve the efficiency of a gas-dynamic pressure wave machine according to the state of the art as is schematically illustrated in FIGS. 1 and 2 by means of different measures.
In a gas-dynamic pressure wave machine according to the state of the art, comprising four channels and no additional control systems such as pockets, which is used in order to supercharge an internal combustion engine, the pressure wave process can only be adjusted for a single operating speed of the internal combustion engine, i.e. the so-called design point of the pressure wave machine. The use of pockets in the housing walls allows a less tuning-sensitive design of the pressure wave machine and a significant extension of its load, speed, and volume range. The disadvantage of this method is that in the range of untuned performance, the pressure wave process is diverted to secondary processes which cannot yield optimum efficiency. The result is an increase of the losses caused by such secondary processes in the pockets, e.g. inflowing and outflowing gases and the production of pressure and expansion waves by the pockets.
The transition from the so-called primary process, also called compression pocket process, to the principal process, i.e. the tuned process, causes disturbances in the pressure wave process which cause scavenging disruptions and thus ranges of increased recirculation of exhaust gas into the charge air. In order to prevent an increased recirculation in these ranges as well as during starting, an inlet leading to the gas pocket, either in the form of a milled sill or of a controlled inlet as disclosed in the above-mentioned document, must be provided, which however produces further losses due to a diversion of high pressure energy into the low pressure process.
The mutual alignment of the openings of the two high-pressure channels, i.e. of the high pressure exhaust channel and of the high pressure charge air channel, is an important regulating variable which can be influenced by the gas pocket, inter alia.
Attempts have been made to control this alignment, e.g. according to DE-B-1 052 626, DE-A-30 40 648, or finally according to U.S. Pat. No. 3,011,487. The cited publications disclose the use of plates or rings having openings and which are provided at the entrance of the mentioned channels to the air resp. to the gas housing, these plates or rings being attached to the respective housings and being mutually adjustable in order to act upon the alignment of the orifices of the high-pressure channels. These devices including plates have the drawback that they involve a complicated construction and cause additional losses due to the plate surfaces which must be sealed.
WO 97/20134 discloses a device for supercharging the charge air of an internal combustion engine by means of a multiple cycle pressure wave machine having a compression slide valve where the opening and the closing edges of the inlet and the outlet opening of the exhaust front housing and the charge air front housing are mutually offset in the direction of rotation of the cell rotor at a predetermined rotation speed of the cell rotor and a exhaust gas temperature. In the embodiment of the pressure wave machine having a compression slide valve, it is suggested to rotate the exhaust front housing. Since this is the high temperature part of the pressure wave machine, a device for the rotation of the exhaust front housing acting on this portion is disadvantageous.
On the background of this prior art, it is a first object of the present invention to provide a gas-dynamic pressure wave machine which allows an adjustment of the process over the entire performance range of the internal combustion engine in a simple manner and without any additional losses due to plate joints, and particularly without a detrimental influence of high temperatures, by a variation of the mutual alignment of the high pressure channel openings. This object is attained according to independent claim 1 or 3.
In order to ensure a high efficiency of the pressure wave machine over the entire speed range of the internal combustion engine by means of the disposition of the edge geometry of the channels at the rotor, it is indispensable to provide a sufficient rotor scavenging of the pressure wave machine at higher motor speeds to prevent an excessive increase of the charge air temperatures. Consequently, in pressure wave machines of the prior art, the width of the openings of the low pressure channels is designed for higher engine speeds, i.e. as wide as possible, while the openings of the high pressure channels are as narrow as possible. For lower to medium engine speeds, temperatures, and flow rates, however, this edge geometry, i.e. wide low pressure channels and narrow high pressure channels, becomes problematic.
On the background of this prior art, it is another object of the invention to improve the charging efficiency of a pressure wave machine in the range of lower to medium engine speeds, temperatures, and flow rates of the internal combustion engine. This object is attained by the pressure wave machine according to independent claim 8.
In known pressure wave machines of the prior art, the rotor runs in a bearing with lifetime lubrication which is exposed to an air current in an inlet of the intake channel of the pressure wave machine and is thereby cooled. The drawback of this system is the heating of the input air resulting from the cooling of the bearing and the disadvantageous configuration of the inlet channels with respect to the flow, which results in a reduced efficiency. Furthermore, it is possible that the cooling of the bearing is no longer ensured e.g. when the internal combustion engine is stopped after a long trip. Moreover, under certain load conditions, the temperature level of the bearing is still so high in spite of the input air cooling that expensive high-temperature lubricants must be used.
The axial clearances between the housings and the rotor greatly influence the efficiency of the pressure wave machine. In the case of excessive play, the gap losses will increase, and if the play is too small, it is possible that the rotor will graze against the housings. In order to reduce the play, the parts may be manufactured from a low-expansion steel alloy. In this case, however, a relatively large clearance must be provided in the cold state, which is disadvantageous in that condition, besides the need for expensive special alloys.
U.S. Pat. No. 2,800,120 discloses a pressure wave supercharger having a water-cooled end plate in which the rotor is journalled on the gas side. However, neither the air side nor the external surface are cooled by this cooling system.
On the background of this prior art, it is further object of the invention to provide an efficient cooling of the rotor resp. of the rotor bearing which eliminates the drawbacks indicated above and therefore allows a further improvement of the efficiency without using expensive alloys. This object is attained by means of the pressure wave machine according to independent claim 12.
Further advantages and embodiments of the pressure wave machine according to the invention are defined in the dependent claims.